The need to communicate data is an endemic necessity of modern society. Data is communicated through operation of a communication system. In a communication system, the data is communicated between a sending a station and a receiving station. The sending and receiving stations are connected together by way of a communication channel.
Data that is to be communicated by the sending station is converted into a form to permit its communication upon the communication channel. When the data is communicated upon the communication channel, the data is delivered to the receiving station. Once delivered at the receiving station, the informational content of the data is recovered.
A wide variety of different types of communication systems have been developed and are regularly utilized to effectuate communication of information between the sending and receiving stations. And, new types of communication systems have been, and continue to be, developed and constructed as a result of advancements in communication technologies.
A radio communication system is exemplary of a type of communication system that has benefited from advancements in communication technologies. In a radio communication system, radio links are utilized upon which to define communication channels that extend between sending and receiving stations operable therein. The need otherwise to utilize fixed, wireline connections upon which to define communication channels is obviated. Reduced infrastructure costs are, accordingly, generally associated with radio communication systems. And, radio communication systems can be constructed to permit one or both of the sending and receiving stations to be mobile.
The radio links, upon which the communication channels are defined, are formed upon a portion of the electromagnetic spectrum. The communication capacity of a radio communication system is, however, sometimes constricted by bandwidth limitations associated with the bandwidth of the electromagnetic spectrum available to a communication system upon which to form communication channels. When the communication capacity of the communication system is constrained in this manner, the communication capacity of the system can be increased only through more efficient utilization of the allocated bandwidth.
Digital communication techniques are implemented in many communication systems, and the use of such techniques permits the communication capacity of a communication system to be increased. The use of digital communication techniques generally permit the bandwidth allocated to the communication system to be utilized more efficiently.
Digital communication techniques typically involve digitizing data that is to be communicated into digital form to form digital bits. The digitized bits are sometimes then formatted into sequences referred to as packets or frames. While different communication systems define the groupings of digital bits in different manners, the terms packet and frame shall, at times, be used interchangeably herein to refer to any set, or group, of digital data that is communicated during operation of a communication system.
Sequences of the data forming the packets or frames can be communicated at discrete intervals and thereafter connected theretogether to recreate the informational content of the data. Because packets or frames of data can be communicated at the discrete intervals, a frequency band need not be dedicated solely for the communication of data generated by one sending station for transmission to one receiving station, as conventionally required in circuit-switched communications. Instead, the frequency band can be shared amongst a plurality of different sending and receiving station pairs. Because the same frequency band, e.g., radio link, can be utilized to effectuate communications by the plurality of pairs of communication stations, improved communication capacity is possible.
Conventional local area networks (LANs) communicate packets of data to effectuate communications between sending and receiving stations defined therein. Wireless networks, operable in manners analogous to LANs, referred to as WLANs (wireless local area networks) have also been developed and are utilized to communicate data over a radio link.
The standards of operation of an exemplary WLAN are set forth in the IEEE (Institute of Electrical and Electronic Engineers) 802.11 specification. The system standard set forth in the specification provides for multi-user communications.
At least one implementation of a WLAN anticipates, or otherwise uses, OFDM (orthogonal frequency division multiplexing) techniques. OFDM effectively forms a hybrid of a multi-carrier modulation (MCM) and frequency shift keying (FSK) modulation. Frequency-divided carrier frequencies are defined in an OFDM system, and the carriers are selected to be orthogonal to one another, such as by separating the carriers by integer multiples of the inverses of symbol durations of parallel bit streams that are to be applied thereto. The orthogonal carriers are transmitted simultaneously thereby permitting an entire allocated channel to be occupied through an aggregated sum of narrow, orthogonal subbands.
Various techniques are used in conventional, wireline communication systems that utilize OFDM. In particular, a so-called, water-filling technique is sometimes utilized to facilitate optimal utilization of the subcarriers defined in the OFDM system. However, such conventional water-filling techniques do not provide a dynamic allocation scheme needed for a radio application. That is, the communication characteristics of channels defined upon a radio link are much more likely to be adaptively alterable due to fading characteristics regularly exhibited upon radio channels. And, a more dynamic allocation scheme than that provided by a water-filling technique for use in a radio communication system.
Accordingly, an improved manner by which to allocate communications on the subcarriers are defined in a communication system, such as a WLAN, that utilizes OFDM techniques would be advantageous.
It is in light of this background information related to communication systems that utilize OFDM, or other multi-carrier modulation techniques, that the significant improvements of the present invention have evolved.